1. Field of the Invention
The invention concerns a hydraulically powered fan for a radiator in a motor vehicle which shares a hydraulic power source with a power steering system.
2. Description of Related Art
In automotive vehicles, a fan commonly removes heat from liquid coolant, by pumping air over a heat exchanger, or radiator, through which the coolant flows. The fan is commonly driven directly by the engine through a power-transmission belt.
However, one problem with such direct-drive of the fan is that fan speed is linked to engine speed: as engine speed increases, the fan speed also increases. However, as engine speed increases, vehicle speed also generally increases. Increased vehicle speed increases the ram air flow through the radiator, which also cools the coolant, thereby reducing the need for fan cooling.
Thus, at high engine speed, in many cases, the fan runs at a high speed, but is not needed. Some fans are equipped with a clutch, which dis-engages them from the engine, at high engine speeds, to solve this problem.
However, even when this fan problem is solved, other factors exist which are undesirable. One is that fans are noisy. Each fan blade, as it passes an observer, delivers a small pressure pulse to the observer. As fan speed increases, the number of blade-passes occurring per second also increases, thereby increasing the number of pulses per second. That is, pulse frequency increases as fan speed increases. In addition, the magnitude of the pulses also increases as speed increases. Thus, a high-speed fan acts as a loud, high-frequency, noise source.
Another problem which arises is not so much attributable to the fan, as to automotive design principles. In a transversely mounted engine, the crankshaft is perpendicular to the direction of travel. However, the cooling face of the radiator is preferably perpendicular to the ram air stream, which is parallel to the direction of travel. If the disc representing the fan blades is parallel to the cooling surface of the radiator, then the fan's rotational axis is perpendicular to the crankshaft, causing complexity in transferring power from the crankshaft to the fan.